title: Demonstration of tyrosinase in the vitiligo skin of human beings by a sensitive fluorometric method as well as by 14C(U)-L-tyrosine incorporation into melanin.
abstract: Tyrosinase activity (Monophenol, dihydroxyphenylalanine: oxygen oxidoreductase EC 1.14.18.1) in vitiligo and normal epidermal homogenates of skin from human beings was measured by estimating beta 3,4-dihydroxyphenylalanine (dopa) by a highly sensitive fluorometric method described in this paper. The tyrosine activity in the vitiligo skin was about 4 to 37% of corresponding normal skin. The activity of tyrosinase in normal human skin from different individuals and from different regions of the body was in the range of 4 to 140 picomoles of beta 3,4-dihydroxyphenylalanine formed per min/mg protein of epidermal homogenate. The enzyme from vitiligo and normal skin was severely inhibited by substance(s) of low molecular weight. The enzyme exhibits a lag of about 4 hr in the absence of added beta 3,4-dihydroxyphenylalanine and 1 hr in presence of 5 microM dopa. Tyrosinase from the normal and vitiligo skin was inhibited by excess concentration of tyrosine. The homogenates from vitiligo skin could synthesize melanin from C14(U)-L-Tyrosine. The rate of tyrosine incorporation into melanin by the epidermal homogenates is increased by 3,4-dihydroxyphenylalanine (dopa) disproportionate to its effect on tyrosinase activity. Based on the data presented in this paper it is concluded that melanocytes are present in the vitiligo skin. A tentative hypothesis is put forward to explain the lack of melanin synthesis by the vitiligo skin under in vivo conditions, although melanocytes are present.
mesh_terms: D002102:Cadaver; D002250:Carbon Radioisotopes; D004156:Catechol Oxidase / Q000032:analysis*; D046508:Culture Techniques; D004295:Dihydroxyphenylalanine / Q000096:biosynthesis; D006801:Humans; D006900:Hydroxylation; D008543:Melanins / Q000096:biosynthesis; D014442:Monophenol Monooxygenase / Q000032:analysis* / Q000378:metabolism; D012867:Skin / Q000201:enzymology*; D013050:Spectrometry, Fluorescence / Q000379:methods; D014443:Tyrosine / Q000378:metabolism; D014820:Vitiligo / Q000201:enzymology*
chemical_list: D002250:Carbon Radioisotopes; D008543:Melanins; D014443:Tyrosine; D004295:Dihydroxyphenylalanine; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase